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Started by ggoerl, December 13, 2017, 12:00:09 PM
Quote from: ggoerl on December 14, 2017, 01:54:22 AMThanks for the response, I ended up going forward and replaced all the capacitors, took me about an hour and a half for the whole process. Unfortunately I'm left with transistors and stuff but have no idea where to replace them as I didn't understand the schematics so well.Also, what is the clear tube next to the bulb, do these go bad?
Quote from: Ben Bove on December 14, 2017, 05:28:47 PMYou may want to look up a basic explanation of transistors online, how to test them with a multimeter etc. or take it to any electronics repair shop with the schematic and ask them to replace the transistors.
Quote from: sean on December 16, 2017, 07:37:56 PMTake the 100uF capacitor that you mis-installed and had to remove, and solder little leg extensions onto it. Just wrap little pieces of wire around the terminals, so that they are long enough to reach the holes in the circuit board. Solder it all together, and you are in business.Sean
Quote from: sean on December 26, 2017, 10:27:55 PMThe 2N3053 is $2.31 on Mouser today. The 2N3053A is the more expensive one. Dunno how your search didn't find the cheap one.(I wonder if 2N3053A's lower Vce saturation voltage is worth worrying about.)Yes, I think that 330pF ceramic disk capacitor from Murata will be fine.And yes, if you get the 2N3392 transistor in the TO-92 plastic package, it will have the same pinout that it has had for 40+ years: E-C-B.None of the diodes are in the audio path, they are in the tremolo oscillator and lamp circuit. Since the schematic says they are "2A diodes", I would buy a few dozen 1N5408 diodes. They are physically the same size as the 1N5401 diodes, but rated to survive much higher reverse voltage. They cost exactly the same as the 1N5401 diodes (unless you buy hundreds of them). The 1N5408 diodes are rated for 3A of current (more than ten times what is needed here). The leftover diodes will come in handy some day.Sean
Quote from: pnoboy on January 10, 2018, 06:53:28 AMIf you have the preamp out of its case, try touching with your finger the spot at which the input from the harp connects to the preamp. If you hear no hum, your problem is likely to still be in the preamp. To be sure, you could unsolder the input wire so that there is no signal connected to the preamp's input. Then, once again touch your finger to the input. If there is still no hum, then your probably is almost surely with the preamp.
Quote from: sean on January 19, 2018, 05:48:06 PMPlease post a fresh photo of the top side and bottom side of your board.Have you checked for sure that the volume, bass, and treble potentiometers are functioning correctly? No open circuits there? No short circuits there?Stop and triple check that every transistor is installed correctly. Follow the traces on the board to verify that they connect to nearby components as shown in the schematic.http://www.fenderrhodes.com/org/ch11/fig11-8.jpgThen spend a little time probing around the board to verify that voltages are reasonable at each transistor. Since they are all NPN transistors, you should get the voltage at the base terminal to be slightly higher than what is measured at the emitter. Vbe should be around .5V to .7V in a happily-biased small-signal transistor.You know that the oscillator section is working, because the lamps are working. So no need to poke around there.It is time to trace the audio through the board step by step. An oscilloscope is easiest, but you can build a little probe to feed audio into your guitar amp, or keyboard amp.Sean